WO 2007/071 383 relates to an apparatus for contactless, redundant position determination, in which two integrated magnetic angle sensor circuits constructed on a Hall sensor basis are placed above one another in a common housing, the two circuits being separated from one another by means of an insulating intermediate layer.
In the case of these angle sensors, a structure in which the axis of rotation of the rotating magnet comes to rest centrally above the center of the integrated Hall sensor group arranged in a circular manner on the circuit is essential. A lateral offset of the sensor elements relative to the axis of rotation results in an increase in the angle error, in particular if the Hall sensors are situated outside the vertical magnetic field Bz running in an approximately linear manner between the poles of the magnetic field source.
For this reason, it is therefore not useful to position the circuits beside one another in a common housing. In order to center both angle sensors relative to the axis of rotation of the magnetic field source, they must therefore be installed above one another in the common housing.
The disadvantage of this structure is the greater amount of effort caused by mounting the circuits above one another with an additional insulation layer in between.
Another disadvantage is that the tolerance range for the vertical distance between the magnet and the sensor housing is greatly restricted by the structure of the angle sensors lying above one another since both the angle sensor lying at the bottom and the angle sensor lying at the top must be within a tolerance window for the optimum operating range of the strength of the magnetic field. Furthermore, this structure is suitable only for an axial structure where the angle sensor circuit is below the magnetic field source in a manner normal and central to the axis of rotation.
In safety-critical applications, for example a drive motor for an electronic steering system EPS, forces may act on the drive shaft to be measured in the event of load changes, for example, which forces displace the drive shaft in the axial direction. As a result of the axial structure, this displacement changes the distance between the magnetic field source, which is fitted at the end of the drive shaft, and the sensor. In order to avoid possible damage to the sensor or magnet caused by mechanical contact between the two objects, a minimum distance between the magnetic field source and the sensor housing must be complied with, which in turn further restricts the tolerance range for the distance between the sensor and the magnetic field source.